Purpose/Significance of Application:Field demonstration of in situ air stripping using horizontal wells to supplement groundwater pump and treat technology.

Regulatory Requirements/Cleanup Goals:
- No specific cleanup goals identified for the field demonstration - Demonstrations permitted by the South Carolina Department of Health and Environmental Control (SCDHEC) Air Quality Control (AQC) and Underground Injection Control (UIC)

Description:At the U.S. Department of Energy Savannah River Site, administrative buildings are located within the A area and aluminum forming and metal finishing operations have been performed within the "M" area. An estimated 3.5 million pounds of solvents were discharged from these operations between 1958 and 1985, with over 2 million pounds sent to an unlined settling basin. Groundwater contamination beneath the settling basin was discovered in 1981. A pump and treat program has been ongoing since 1985 for removal of VOCs from the groundwater.

A field demonstration using in situ air stripping with horizontal wells in the A/M Area was conducted from July 1990 to September 1993. The demonstration was part of a program at Savannah River to investigate the use of several technologies to enhance the pump and treat system. In the air stripping demonstration, air was injected into a lower horizontal well in the saturated zone and extracted through the horizontal well in the vadose zone. The demonstration did not include treatment of offgases. The in situ air stripping process increased VOC removal over conventional vacuum extraction from 109 pounds per day to 129 pounds per day. Nearly 16,000 pounds of VOCs were removed during the 139 day demonstration period.

A cost analysis performed as part of this demonstration showed that in situ air stripping would reduce costs by 40% over a conventional pump and treat with soil vapor extraction system. Installation costs for horizontal wells is greater than for vertical wells. At depths greater than 40 to 50 feet, horizontal well installation costs are approximately $200/ft; at less than 40 to 50 ft, costs are as low as $50/ft. Several implementation concerns were identified for installing horizontal wells at Savannah River.

can remove VOCs for approximately 69% of the cost for conventional methods. Installation costs for horizontal wells is greater than for vertical wells. For deeper horizontal wells (over 40-50 feet), costs range from $360 to $700 per foot. Several implementation concerns were identified for installing horizontal wells at Savannah River.